(1) Field of the Invention
The invention relates to a heat-resistant lining for a wall, such as the bulkhead between the engine compartment and the cabin of a helicopter, and to a wall lined with the lining of the invention.
(2) Description of the Prior Art
The walls surrounding the space in which the engine or power mechanism of a helicopter is contained may be made of glass fiber-reinforced plastic sheet. In instances where, due to heat generated by the engine or power mechanism the wall may be subjected to a temperature in excess of 200.degree. C., some form of protection for the wall is necessary, because temperature in excess of 200.degree. C. may harm the wall material. Further, some form of wall protection is deemed desirable especially where the wall serves as a bulkhead between the engine or power mechanism compartment and the cabin for the pilot, so that in case a fire starts in the engine or power mechanism compartment it will be contained therein for a certain period of time without spreading to the cabin. For instance, it may be required that the bulkhead be lined on the side facing the engine or power mechanism with a lining that will withstand a temperature of 1100.degree. C. for at least five minutes without any local destruction and without any change in position of the lining relative to the wall.
A particular problem exists in the art, in trying to find a lining material which simultaneously meets all the design criteria. For instance, the desirable lining material would prevent the inside surface of the protected wall from reaching a temperature of 200.degree. C. even when the operating temperature within the engine or power mechanism compartment usually is at a level of 250.degree. C. The same lining material would have the above-described stability and persistance in case of fire, and be able to be attached to the wall in such a way that no damage occurs to the wall or to the lining as the lining is being installed and used, even where the wall is not flat but is irregularly configured. In particular, the lining should closely follow any irregularities in the form of the wall. Heretofore, an asbestos cardboard material has been used as the liner for such walls, the asbestos cardboard being covered on one face with an adhesive for adhering it to the inside surface of the wall that is to be protected and covered on its exposed face with a known type of paint which foams when exposed to a conflagration. Usually this paint is, in turn, covered with a layer of clear polyurethane lacquer, in order to seal the paint against attack by moisture.
This known lining material is of merely conditional suitability. One problem is with adhesion; the asbestos cardboard material adheres poorly to the inside surface of the wall and, in the case of mechanical shock, e.g. vibration, is inclined to peel off from the wall. Another problem is with the paint. The paint is designed to start its foaming reaction when subjected to a temperature that is only slightly above 200.degree. C. The lacquer coating may be only partially successful in preventing the paint from reaching its foaming temperature under normal operating conditions. As a consequence, here and there, in local sites, the paint gets too hot and foams-up, locally destroying the polyurethane covering and thus subjecting more of the paint to heat and moisture causing more premature foaming of the fire-protective paint.